1. Field of the Invention
The present invention relates to optoelectronic transceivers, and more particularly to a optoelectronic transceivers fabricated to be reduced in size and manufacturing complexity.
2. Description of the Related Art
Conventional duplex fiber optic connectors, such as SC Duplex connectors, (see, for example, ANSI Fibre Channel--physical and signaling interface (FC-PH) X3.230 rev. 4.3 (1994)) achieve the required alignment tolerances by threading each optical fiber through a precision ceramic ferrule. The two ferrules of an SC connector have an outer diameter of 2.5 mm, and the resulting fiber-to-fiber spacing (or pitch) of a duplex connector is approximately 12.5 mm, i.e., the distance from ferrule face to ferrule face when in operative position in the connector. Since the outer of the fiber captured by the ferrule is only 125 .mu.m, it should be possible to design a significantly smaller optical connector. Smaller connectors with fewer precision parts could dramatically reduce manufacturing costs.
Recently, a new class of "small form factor" (SFF) fiber optic connectors has been introduced with the goal of reducing the size of a fiber optic connector to one half of that of a standard SC Duplex connector while maintaining or reducing the cost. Such connectors are described by C. Schwantes, in "Small form factors herald the next generation of optical connectors", Lightwave, October 1998, pp. 65-68. Several different designs have been proposed by different manufacturers, including the LC (manufactured by Lucent Technologies and others), MT-RJ (manufactured by Fujikura, Siecor and AMP and others), and VF-45 (manufactured by 3M Corp.). All connectors use the familiar RJ45 modular jack latching mechanism used in telephone cords for securing the connector.
While the smaller size of the SFF connectors is in itself an important advantage, an equally important advantage of the new SFF technology lies in the corresponding smaller size of the transceivers which mate to these connectors. The transceiver is a module including a digitally modulated laser to feed light signals into the outgoing fiber of the mating SFF connector, as well as a detector which receives light signals from the incoming fiber of that detector. The transceiver also includes the electronic chips which process these signals for both the transmitting and receiving functions, and provide connections between the module and a "master" board to which it is connected.
The smaller SFF transceiver size means that less area on the board is occupied, which permits the user to install more interconnects. A SFF Multisourcing Agreement between major manufactures of optical transceivers specifies a 13.97 mm pitch requirement between ferrules for the transceivers, a maximum length requirement for the transceivers of 31 mm, and a maximum height of 9.8 mm, which in effect permits a doubling of the port density compared with transceivers designed to mate to SC Duplex connectors.
Careful attention is needed to design a SFF transceiver to ensure full functionality while maintaining a low cost. A critical component of the transceiver is the optical subassembly (OSA) which carries out the conversion of electrical to optical signals (transmitter optical subassembly, TOSA), or optical to electrical signals (receiver optical subassembly, ROSA). The optoelectronic chips, i.e. laser (transmitter) and detector (receiver) are usually housed in metal "TO" cans furnished with a window for light transmission, so that the chips are hermetically sealed. The fabrication of an optical system which serves to align the fibers to the chips in the cans while efficiently permitting optical power transfer represents a difficult challenge in the design of all OSAs.
Therefore, a need exists for OSAs which are smaller in size and easier to manufacture. In particular, a need exists for OSAs which mate to connectors with a small, 1.25 mm diameter ferrule, e.g. the LC connector.